Plastic bottles are widely used as containers for retailing soft drinks and other beverages. One type of plastic, polyethylene terephthalate (PET), has become particularly popular because of its transparency, light weight, and low cost. In addition to being flexible, the walls of PET bottles are strong in tension and thus can safely contain the pressure of a carbonated beverage. Moreover, conventional PET bottles can bear surprisingly high compressive loads, provided that the load is directed substantially along an axially symmetric axis of the bottle. A single PET bottle can support the weight of many bottles of the same size filled with beverage if the bottle is standing upright on a flat, horizontal surface and the weight of the other bottles is applied to the closure of the single bottle and is directed substantially vertically along the symmetric axis. However, if a compressive load is applied to a conventional PET beverage bottle along a direction other than the symmetry axis of the bottle, the bottle tends to buckle. This tendency of conventional PET bottles to give way under off-axis compressive loads is particularly pronounced for large capacity bottles, such as the two-liter bottle widely used for marketing soft drinks.
Soft drink bottles are ordinarily packaged by bottlers in cases or other containers, several bottles to the case, for shipment to retailers or for storage. The term “case”, “crate” or “tray” is used interchangeably herein to include all cases, crates, trays and similar containers having a bottom and peripheral side wall structure. Cases of bottles are customarily stacked on top of each other. In storage warehouses, columns of cases are frequently stacked on pallets which can be lifted and moved about by fork-lift trucks. The stacks of cases on the pallets must therefore be particularly stable in order to remain standing in the face of the jostling inherent in being moved about. A technique for interconnecting stacks of empty cases, called “cross-stacking,” is often used to improve the stability of empty cases loaded on a warehouse pallet. Cross-stacking generally involves stacking rectangular bottle cases to build up a layered structure, with each layer having cases oriented parallel to each other and with the adjacent layers being oriented at right angles to each other. Thus, since the adjacent layers are perpendicular, each case in the cross-stacked layer rests on at least two cases in the layer below. As a result, the cases of the cross-stacked layer tend to keep the cases on which they rest from moving apart from each other. The cross-stacked layers therefore stabilize the stacked structure.
Because of the tendency of conventional PET beverage bottles to buckle under off-axis loads, attempts to stack cases of these bottles give rise to serious problems. Bottles can tilt away from vertical alignment upon stacking if conventional partitioned cases having low side walls are used to contain the bottles. Tilted bottles in the lower cases of a stack can buckle and give way, causing the stack to fall. Even absent buckling, the tendency of bottles to tilt in conventional low-sided cases causes problems. Tilting generally places an undesirably low limit on the number of tiers in a stack since the tilting of bottles in one case can cause the next higher case in the stack to tilt. This leads to instability if too many tiers are included in the stack.
Previously, these problems were dealt with by packaging beverage bottles in corrugated-paper cartons having high sides, often equal in height to the height of the bottles. Two-liter PET bottles filled with soft drinks were often packaged in enclosed corrugated paper cartons for storage and shipment. Although the high sides of these paper cartons reduce the incidence of tilting and provide additional support when the cartons are stacked, the cartons are expensive. The cost of the cartons cannot ordinarily be distributed over a number of repeated uses since corrugated-paper cartons generally are not rugged enough for reuse and therefore they are usually discarded by the retailer. The cartons also do not generally provide viewing of the products there within and, thus, even the cartons loaded with bottles are not easily identifiable with a particular soft drink bottler.
One solution to the problems of full depth corrugated-paper cartons is plastic full depth cases; that is, plastic cases having peripheral sidewalls approximately the same height as the bottles. In plastic full depth cases, the sidewalls are the load bearing surfaces. Full depth plastic cases, however, have numerous disadvantages. They are expensive to manufacture, they are expensive to ship and to store empty in a warehouse as they require a large amount of space. Full depth cases also totally surround the bottles and prevent display of the bottles and are not easily identifiable with a particular product or supplier, except by the imprinted or painted logos or other insignia that may be applied thereto.
To overcome these problems plastic low depth cases have been used. A low depth case is one in which the side walls are lower than the height of the stored bottles, and in which the bottles support the weight of additional cases stacked on top. The commonly assigned U.S. Pat. Nos. 4,899,874 and 4,978,002, the contents of which are hereby incorporated by reference, disclose a low depth bottle case for two-liter bottles that is cross-stackable when empty if the upper cross-stacked cases are properly positioned. In addition, in the embodiment disclosed the substantially flat upper surface across the bottle retaining pockets permits one piece petaloid bottles and bottles with base indentations to be retained. The low height of the case sidewalls and the columns above the case sidewalls also allow the display of the bottle labels to the consumer. The side walls, however, are generally rectangular and do not identify the particular supplier of the soft drink, except by imprinted or painted logos or insignias that may be provided.